Practicality of fade-in/out transforms in Blender
The vse is quite powerful but you need to realise that it is media agnostic.  That is any track can accommodate any media. Because audio can be next to or above video you cannot easily add an effect at an edit point. And because there are effectively infinite vertical tracks you need to tell blender which media strips need to be used for an effect.

That is why you must first select the strips to effect then add an effect. If you want to fade from many mixed clips to black for example you would simply key frame the opacity of the top most in coming black strip.